If you describe a person or their actions as unprincipled, you are criticizing them for their lack of moral principles and because they do things which are immoral or dishonest. [disapproval]
It is a market where people can be very unprincipled and unpleasant.
...the unprincipled behaviour of the prosecutor's office during the crisis.
Synonyms: dishonest, corrupt, crooked [informal], immoral